1. Field of Invention
This invention relates to a cable assembly in which removal of the protective jacket or sheath can be facilitated by having the ripcords attached to a tape in the cable assembly, which provides access to the underlying core. The ripcords placement in the cable assembly is also used as means for improving the ability of the cable assembly to withstand bending by using ripcords with excess length. The invention is particularly useful in optical cable assemblies, which have a tendency to be crush sensitive, and also other telecommunications cable assemblies including those containing fragile elements, such as copper wires insulated with thin, low resistance plastic such as cellular Pe.
2. Related Art
Ripcords are used within a cable assembly to facilitate removal of a protective jacket or sheath, thus allowing direct access to the cable cores. Ripcords are generally introduced under the armor at the forming station (armored cables) or over the cable core at the jacket extruder head (dielectric cables) during the manufacture of a cable. The ripcords are disposed through the cable longitudinally or in a helical fashion having a long pitch. When two ripcords are provided, they are typically aligned to be 180 degrees apart, thereby potentially allowing for the cable jacket or sheath to be perfectly bisected. However, maintaining the position of the ripcords at 180 degrees becomes difficult during the manufacture of the cable assembly. Difficulties in maintaining the position of the ripcords can be, among other things, caused by core rotation relative to the armor, armor rotation relative to the cable sheath, intermittent sticking and slipping between the ripcords and the armor as the armor is formed, and/or inadequate ripcord pay-off tension.
The movement of the ripcords out of their initial position reduces functionality of the ripcord for a number of reasons. Among these reasons, ripcords that become positioned too close to the sharp edges of armor tape used in the manufacture of the cable can be cut, or they can xe2x80x9cescapexe2x80x9d from their desired location from under to over the armor. Also, if the ripcords move very close to each other, only a narrow slot (if no slot at all, as the second ripcord will slide through the opening created by the first one) is cut through the jacket or sheath, thus making extraction of the cable core very difficult.
A second problem in the prior art arises when the cable becomes bent. In this situation, ripcords that do not have excess length (that is, ripcords with a length that is nearly equal to the cable length) and which are not located on a neutral axis of the cable, are subjected to forces which tend to pull the ripcord toward the neutral axis of the cable. This stress of the ripcord may squeeze the cable core and damage, for example, the buffer tubes or optical fibers underneath, possibly causing attenuation increase or mechanical damage to the fiber coating. This is more particularly likely to happen in cable structures that have a tight fit between the core and the sheath/jacket, thus limiting the possibilities for the ripcord to move around the core to reach the cable neutral bending plane. The present invention overcomes these problems.
It is an object of the present invention to provide a cable assembly in which the ripcords are attached to the tape by, for example, bonding or weaving the ripcords to the tape, thus preventing movement of the ripcords from their initial position.
It is another object of the invention to provide a cable assembly having at least one ripcord with excess length disposed in the cable, which allows bending of the cable assembly with reduced ripcord tension.
Accordingly, the present invention provides a cable assembly comprising a cable core, a tape surrounding the cable core, at least one ripcord attached to the tape, and a cable jacket surrounding the tape. In addition to the cable jacket, the present invention can include a cable sheath disposed between the tape and the cable jacket for providing further protection to the cable core. As an example, a jacket referred to in this context can be a simple extruded plastic layer, while a sheath can represent a more complex protection (e.g., a sheath with additional reinforcement, such as an armor, a tape, or mechanical reinforcement). More particularly, the present invention comprises a cable assembly wherein the ripcord is attached to the tape by bonding or weaving the ripcord to the tape, thus providing for more secure placement of the ripcord and providing additional strength to the tape.
In a second embodiment of the present invention, a cable assembly comprises a cable core having a predetermined axial length, a cable jacket for housing the cable core along the predetermined axial length of the cable core, and a ripcord disposed between the cable core and the cable jacket along the predetermined axial length, in a manner that the ripcord is contained within the predetermined axial length, but the ripcord has a length substantially longer that the predetermined axial length. In a preferred embodiment of the present invention, the ripcord is disposed along the predetermined axial length in a wavy shape, for example sinusoidal, thus the ripcord is made xe2x80x9cflexiblexe2x80x9d, alleviating damage to the cable assembly that can occur from ripcord tension created by bending. When the cable returns from its bent position to a straight position, the ripcords can move back to their original path or locally buckle to accommodate a different path as they usually have a flexural stiffness that is low enough to easily allow this.